1. Field of the Invention
The present invention is related to an optical disk reproducing apparatus and a reproducing method for reproducing music and moving pictures recorded on an optical disk such as a compact disk (CD), a video CD, and a laser disk (LD). More specifically, the present invention is directed to a technique for reproducing information recorded on head portions of the respective tracks of such an optical disk.
2. Description of the Related Art
In this sort of optical disk, for instance, a video CD, a plurality of tracks are formed, and the respective tracks are accessible by using track numbers. It should be noted in this specification that a track designated by a track number "n (n=0 to 99)" will be referred to as a track "n". Also, the term "track" implies a logical track unless a special definition is made. A track "0" provided at an innermost peripheral portion of this video CD is referred to as a read-in area, and TOC (Table of Contents) information is stored in this read-in area. This TOC information is arranged by the track numbers of the respective tracks, and data indicative of starting positions of the respective tracks expressed by the MSF format.
It should also be noted that an "MSF" format corresponds to a data format used to designate a position on an optical disk. Symbol "M" indicates "Minute", symbol "S" represents "Second (S=00 to 59)", and symbol "F" shows "Frame (F=00 to 74)". For example, a position on an optical disk is designated by "00:04:24" (implies 0 minute, 4 seconds, 24 frames). It should also be understood that 1 (one) frame corresponds to 1 (one) sector.
In the case that the information recorded on such an optical disk is reproduced, signals read from this optical disk contain a signal representative of music and moving pictures in a CD-ROM format, and an SUBQ signal used to control reading operation of the optical disk.
As indicated in FIG. 1A, in a CD-ROM formatted signal, 1 block is constituted by 2,352 bytes. 1 block contains a 12-byte sync (synchronization) signal portion, a 4-byte header portion, and a 2,336-byte user data portion. The header portion is arranged by a block address portion, and a mode flag portion. On the block address portion, a position of this block on an optical disk is recorded by way of absolute time expressed by the MSF format. On the mode flag portion, information used to define a structure of the user data portion is recorded. On the user data portion, data indicative of music and moving pictures is recorded.
The SUBQ signal corresponds to a signal of a channel Q of a sub-code. The SUBQ signals own signal formats differ from each other in a read-in area, and other areas (namely, a program area and a read-out area). FIG. 1B shows the format of the SUBQ signal acquired from the read-in area, and this SUBQ signal is constructed of 12 bytes. A CONTROL portion (4 bits) is used to designate a sort of a track. An ADR (4 bits) is used to designate a mode. FIG. 1B and FIG. 1C indicate a case of a mode 1. A "00" portion (8 bits) indicates a track number (fixed to zero) of the read-in area. A POINT portion (8 bits) is used to designate a track. A MIN portion (8 bits), a SEC portion (8 bits), and a FRAME portion (8 bits) are used to designate travel time RMSF in a track, and the travel time RMSF represented by relative time where a starting point of the track is set to zero. In a ZERO portion (8 bits), "0" is continuously stored. A PMIN portion (8 bits), a PSEC portion (8 bits), and a PFRAME portion (8 bits) correspond to absolute time instants where a starting point of a program area is set to zero, and are used to designate a time instant PMSF indicative of a starting point of a track designated by the POINT portion. In a CRC portion (16 bits), a CRC code for checking an error is stored.
FIG. 1C represents the format of the SUBQ signal acquired from the program area and the read-out area, which is constituted by 12 bytes. A TNO portion (8 bits) is used to designate tracks in the program area and the read-out area. An INDEX portion (8 bits) is used to designate subdivided areas within a track. An AMIN portion (8 bits), an ASEC portion (8 bits), and a AFRAME portion (8 bits) correspond to absolute time where a starting point of the program area is set to zero, and are used to designate a travel time AMSF within the disk. Other portions of the SUBQ signal are identical to those as explained above.
On the other hand, as a method for reproducing music and moving pictures stored in this sort of optical disk, there are three sorts of reproducing methods. That is, a "normal reproducing methods" for reproducing information recorded on tracks sequentially from a track 1, a "program reproducing methods" for reproducing the information in accordance with a previously programmed sequence, and a "random reproducing method" for selecting an arbitrary track at random to reproduce information recorded on this selected track.
To execute such a reproducing operation, a process for designating a track is carried out. In this track designating process, seek time is calculated so as to execute up/down operation and jump operation of tracks. In this specification, "seek time" implies time required seeking a target position in order to read out data stored at this target position on an optical disk which managed by MSF in the case of a CD. Basically, this seek time corresponds to travel time of an optical pick-up to the above-described target position. This seek time is calculated based on time information contained in the TOC information.
Also, in the case of the "program reproducing method", and in the case that an automatic editing function equal to an automatic program reproducing method responding to a tape length in a cassette deck assemble type system is employed, total time required to reproduce information by using the program reproducing method is calculated. In this case, reproducing time of a certain track "n" is calculated based on the following formula:
reproducing time of track "n"=(time instant PMSF contained in TOC information corresponding to track "n+1")-(time instant PMSF contained in TOC information corresponding to track "n").
In accordance with the standards (will be referred to as "old standards" hereinafter) issued before the present standards related to the video CD, every time information recorded on a track is reproduced, disk information must be read out which is equal to the format information required to reproduce the video CD, and is stored at a head of this reproduced track. As a result, every time the reproducing operation of the information recorded on one track is accomplished, the seeking operation is carried out only during time defined in accordance with the TOC information.
FIG. 2A indicates travel time within tracks, expressed by absolute time where a starting point (namely, head of track 1) of a program area is set as zero. The respective tracks are constructed of subdivided areas designated by index numbers IND0, IND1, - - - , and a head time instant of each area is designated by an INDEX portion of an SUBQ signal. As indicated in FIG. 2B, according to the present standards, the head time instant of the area designated by index number IND1 is contained in the TOC information as a time instant PMSF indicative of the starting point of the track. Also, as represented in FIG. 2C, generally speaking, the area designated by the index number IND0 which is provided at the head of each track is defined as a silent portion having a time period of on the order of 2 seconds, taking account of editing operation of a cassette tape. However, since there is no specific definition of the time period for this silent portion, information may be recorded within a recordable time range of an optical disk.
However, in accordance with the present standards, since the seek time is produced based of the time instant of the index number IND1 included in the TOC information, the head time instant of the area designated by the index number IND0 is neglected. As a result, even when any data is present in the area designated by the index number IND0, this data cannot be reproduced.
Also, in a CD, since the present standards are specified by that seek time required performing a track jump operation is formed based on the TOC information, data recorded in an area designated by the index number IND0 cannot be reproduced only when data is reproduced after a track jump. For instance, in FIG. 2A, in the case that the optical pick-up jumps to the track 3, since the data reproduction is commenced from a time instant 10:00 relating to an area designated by the index number IND1 of the track 3, no data can be reproduced during time instants 08:00 to 10:00 relating to the area designated by the index number IND0.
Generally speaking, in a recommended video CD, there is no data to be reproduced in an area designated by an index number IND0. However, in a certain market, since there is a special optical disk differed from a recommended optical disk, namely, such an optical disk that data is present at an area designated by the index number IND0 is commercially available, any user desires to normally reproduce even such a special optical disk.
Also, as previously explained, when a program reproducing function and an automatic editing function are utilized, total reproduction time is calculated. In such a case that a travel time of an area designated by an index number IND0 of a track "n" is different from a travel time of an area designated by an index number IND0 of a track "n+1", actual reproduction time cannot be calculated. For example, when the reproduction time of the track 3 is calculated, the head time instant of the area designated by the index number IND1 of the track 3 is subtracted from the head time instant of the area designated by the index number IND1 of the track 4. As a result, the reproduction time of this track 3 is equal to 12:02-10:00=02:02, which is completely different from the actual reproduction time, i.e., 12:00-08:00=04:00.
Japanese Laid-open Patent Disclosure JP-A-Showa 62-46478 discloses "Information recording disk reproducing apparatus" as the related art. In this information recording disk reproducing apparatus, when the head time instants of the respective tracks recorded on the read-in tracks are read out to be stored into the memory, in such a case that a plurality of tracks belong to a predetermined time width, only the head time instant of one track is stored. Then, when the head reading of the track is instructed, a target track is searched based on this stored head time instant. In accordance with this information recording disk reproducing apparatus, since the head time instants of all of the tracks need not be stored into the memory, the storage capacity of this memory can be reduced. However, this conventional technique cannot read the data recorded on the area designated by the index number IND0.
Also, Japanese Laid-open Patent Disclosure JP-A-Heisei 7-73084 discloses the compact disk memory retrieving apparatus. This compact disk memory retrieving apparatus sequentially executes the process operation for reading the index data from the compact disk (CD) in unit of 1 block, and the retrieve operation for retrieving target data from 1 block data of this read index data in a parallel manner. In accordance with this compact disk memory retrieving apparatus, the index data can be retrieved in high speed. However, similar to the above-described conventional information recording disk reproducing apparatus, the data recorded on the area designated by the index number IND0 cannot be read.